AbstractDisordered crystallization and poor phase stability of mixed halide perovskite films are still the main factors that compromise the performance of inverted wide bandgap (WBG; 1.77 eV) perovskite solar cells (PSCs). Great difficulties are evidenced due to the very different crystallization rates between I‐ and Br‐based perovskite components through DMSO‐alone assisted anti‐solvent process. Here, a zwitterionic additive strategy is reported for finely regulating the crystal growth of Cs0.2FA0.8Pb(I0.6Br0.4)3, thereby obtaining high‐performance PSCs. The aminoethanesulfonic acid (AESA) is introduced to form hydrogen bonds and strong PbO bonds with perovskite precursors, realizing the complete coordination with both the organic (FAI) and inorganic (CsI, PbI2, PbBr2) components, balancing their complexation effects, and realizing AESA‐guided fast nucleation and retarded crystallization processes. This treatment substantially promotes homogeneous crystal growth of I‐ and Br‐based perovskite components. Besides, this uniformly distributed AESA passivates the defects and inhibits the photo‐induced halide segregation effectively. This strategy generates a record efficiency of 19.66%, with a Voc of 1.25 V and FF of 83.7% for an MA‐free WBG p‐i‐n device at 1.77 eV. The unencapsulated devices display impressive humidity stability at 30 ± 5% RH for 1000 h and much improved continuous operation stability at MPP for 300 h.